Motor vehicle with hybrid drive

ABSTRACT

Motor vehicle having a hybrid drive and a fuel cell system. When activated, the fuel cell system can be operated continuously in a predetermined operating range or at a predetermined operating point of high efficiency, whereby any excess energy generated can be supplied to a power consuming device to maintain the high power withdrawal from the fuel cell system required for said high efficiency.

This application claims the priority of German application no.10227530.0, filed Jun. 20, 2002, and PCT International PatentApplication No. PCT/EP03/04482, filed Apr. 30, 2003, the disclosure ofwhich is expressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to a motor vehicle with an internal combustionengine and a fuel cell.

Specifically, this invention relates to a motor vehicle comprising ahybrid drive device with an internal combustion engine and with at leastone electric machine, at least one electric energy storage mechanism andone fuel cell system for supplying electricity.

Furthermore, this invention relates to a method for operating such amotor vehicle.

A motor vehicle and a method of this type are known from German PatentDE 199 13 794 A1 (Corresponding to U.S. Pat. No. 6,276,473). The knownmotor vehicle has an internal combustion engine which can drive themotor vehicle immediately after starting the vehicle electric system andan electric motor as the main drive motor which receives its power froma fuel cell system. The motor vehicle is driven by the electric motorinstead of the internal combustion engine as soon as the fuel cellsystem has reached operating temperature due to heating of the exhaustgas of the internal combustion engine. After the fuel cell system hasreached the operating temperature, the motor vehicle can be driven bythe electric motor and/or by the internal combustion engine. From thepower generated by the fuel cell system, secondary units of the motorvehicle and units of the fuel cell system can be supplied with theelectric power which is needed to operate the at least one fuel cell ofthe fuel cell system.

WO 98/40922 describes a motor vehicle having a hybrid power generatingsystem comprising a fuel cell system and an internal combustion engine.Hydrocarbon fuel is first cleaved in a pyrolysis reactor to form a fuelcomponent containing hydrogen and the remaining fuel. The at least onefuel cell of the fuel cell system is operated with thehydrogen-containing fraction, supplying electric power for the electricmotor. The remaining fuel may be used as fuel for the internalcombustion engine. The fuel cell system is designed to supply approx.50% of the max. power to be supplied by the hybrid vehicle. In alow-load range, the fuel cell system supplies all or most of therequired power. At a higher load, the internal combustion engine is alsooperated. The internal combustion engine can be used directly fordriving the vehicle wheels or for driving an electric generator whichgenerates power for a single electric motor.

This invention is intended to achieve the object of reducing the powerconsumption of a motor vehicle by using a fuel cell system. This objectis achieved according to this invention by a motor vehicle having aninternal combustion engine, at least one electric machine, at least oneelectric energy storage mechanism; and a fuel cell system for generatingelectric power, and by a method for operating the same.

Accordingly, this object is achieved by the fact that the fuel cellsystem is designed as an auxiliary power source for delivering a lowerpower than the internal combustion engine; a control device is providedso that in its activated state, the fuel cell system can be operatedcontinuously in a predetermined operating range or at a predeterminedoperating point of high efficiency, whereby the power it can deliver canbe supplied to at least one power consuming device, and any excess powergenerated by the fuel cell system can be supplied to at least oneadditional power consuming device to obtain the high power delivery bythe fuel cell system as required to achieve the high efficiencymentioned above. Therefore, the fuel cell system forms an auxiliarypower unit.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a motor vehicle according to an embodiment of the presentinvention having a parallel hybrid drive,

FIG. 2 shows schematically another embodiment of a motor vehicleaccording to this invention with a serial hybrid drive,

FIG. 3 shows a diagram which illustrates the functional relationshipbetween efficiency and power delivered by a fuel cell system inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

The motor vehicle 2 depicted in FIG. 1 contains a parallel hybrid drivedevice 4 having an internal combustion engine 6 and at least oneelectric machine 8 and/or 10. Furthermore, at least one energy storagemechanism 12 is provided for storing electric power, and a fuel cellsystem 14 is provided for generating electric power and preferably alsofor generating usable thermal energy. The energy storage mechanism 12may be a battery, for example, or a capacitor.

The internal combustion engine 6 is connected via a drive train 16 to anautomotive transmission 18 and can drive the vehicle wheels 20 via thistransmission. Additional vehicle wheels 22 may be driven in the same wayor may be non-driven wheels.

The second electric machine 10 is in the drive train 16. When operatedas an electric motor, it can drive the vehicle wheels 20 in addition toor instead of the wheels being driven by the internal combustion enginevia the automotive transmission 18. Preferably a first shiftable clutch18 and/or a second shiftable clutch 21 is provided in at least one ofthe two line sections 16-1 and/or 16-2 between the second electricmachine 10 and the internal combustion engine 6 and/or this secondelectric machine 10 and the automotive transmission 18. When the firstclutch 18 is disengaged and the second clutch 21 is engaged at the sametime, the second electric machine 10 (a) may function as an electricmotor to transmit electric power from the energy storage mechanism 12and/or the fuel cell system and to transmit driving torque to thevehicle wheels 20 without entraining the internal combustion engine 6,or (b) may function as an electric generator which is driven by thevehicle wheels 20 to generate electric current which is stored in theenergy storage mechanism 12 and/or can be transmitted to auxiliary units22 and/or 24, or (c) may be operated as an electromagnetic vehiclebrake. When the second clutch 21 is disengaged and the first clutch 18is engaged at the same time, the second electric machine 10 may be (a)driven by the internal combustion engine 6 and thereby generate electricpower by functioning as a generator, said electric power being storablein the energy storage mechanism 12 and/or able to be supplied to thesecondary units 22 and 24, or (b) used as a starter for starting theinternal combustion engine 6.

As an electric motor, the first electric machine 8 can obtain electricpower from the energy storage mechanism 12 and/or from the fuel cellsystem 14 and transmit torque via the automotive transmission 18 to thevehicle wheels 20, either alone or together with the second electricmachine 10, which is operated as an electric motor, and/or together withthe internal combustion engine 6. Furthermore, the first electricmachine 8 can be driven by the vehicle wheels 20 and can therebygenerate electric current which can be stored in the energy storagemechanism 12 and/or can be supplied to the secondary units 22, 24 and/orauxiliary units of the fuel cell system 14 that are necessary foroperation of its at least one fuel cell, e.g., compressor, heating orair conditioning system, fan, valves.

The electric current is distributed among the various elements by anelectronic control unit 30 of a vehicle electric system 28. Afterturning on the electric vehicle electric system and thus also thecontrol unit 30, the motor vehicle 2 can be started immediately with theinternal combustion engine 6. The resulting heat generated by theinternal combustion engine, e.g., by its exhaust, can be used to heatthe fuel cell system 14 to operating temperature. Instead of or inaddition to that, a heating device may also be provided for heating thefuel cell system 14. After the fuel cell system 14 has reached operatingtemperature, its electric power may be used exclusively or additionallyto provide mechanical energy to the internal combustion engine 6 todrive the motor vehicle 2.

Double arrows 32 and single arrows 34 indicate on the electricconnecting paths between the individual parts in the drawings show thedirection of electric current flow. The double arrows 32 show that thecurrent can flow in either one direction or the other depending onwhether the respective parts are supplying or are being supplied withelectric power.

According to this invention, the fuel cell system 14 is designed as anauxiliary power source for delivering a lower power than the internalcombustion engine 6 and through the control unit 30, when the vehicleelectric system is turned on, the fuel cell system 14 can be operatedcontinuously in a predetermined operating range or at a predeterminedoperating point of high efficiency, in which case the power that can bedelivered by the fuel cell system can be supplied to at least onepreselected unit of the following power consuming devices: electricmachine 8, 10, power storage device 12 and/or secondary units 22, 24,vehicle electric system 28 and control unit 30 and any excess powergenerated by the fuel cell system 14 can be supplied to at least oneadditional unit of these power consuming units, depending onpredetermined operating criteria such as the charge status of theelectric energy storage mechanism 12 and the instantaneous power demandof the other power consuming units.

According to a preferred embodiment of this invention, the fuel cellsystem 14 is designed only for the maximum power demand of the vehicleelectric system 28 and at least one of the secondary units 22, 24. Thesecondary units 22, 24 not only deliver automotive driving power butalso serve other functions such as the operation of the air conditioningsystem, interior heating, seat heating, cigarette lighter, radio,television, navigation system, data processing system, ice chest orrefrigerator, window opener, door opener, sunroof or convertible topopener, trunk opener, vehicle steering, vehicle brake system, vehicleinterior lighting, vehicle exterior lighting, telecommunication systems,compressor, oil pump, water pump and/or gasoline pump and/or a toolunit, in particular a cable winch, vehicle lift and/or a street sweeperbrush.

According to a preferred embodiment of this invention, the maximumefficiency of the fuel cell system 14 is in the predetermined operatingrange or at the predetermined operating point.

Similar parts in FIG. 2 are labeled with the same reference notation asthat used in FIG. 1. A generator 40 has or can have a drive connectionto an internal combustion engine 6 through a drive connection 42 forgeneration of electric power and it is or can be electrically connectedvia an electric or electronic control unit 30 of the vehicle electricsystem 28 to the electric energy storage mechanism 12 and/or an electricmachine 10. The electric machine 10 is or can be connected electricallyto the generator 40 or to the electric energy storage mechanism 12(e.g., a battery or a capacitor) either directly or preferably via thecontrol unit 30. The electric machine 10 has a drive connection to thevehicle wheels 20 via a drive train section 16-2 or it can be connectedthereto via a shiftable clutch 21. The drive train section 16-2 maycontain a transmission.

The generator 40 is preferably also operable as an electric motor forstarting the internal combustion engine 6.

When the electric machine 10 is supplied with electric current from theenergy storage mechanism 12 or the generator 40, it acts as an electricdrive motor for driving the vehicle. Furthermore, this electric machine10, when it is driven by the vehicle wheels 20 when the vehicle iscoasting, can function as a generator and thereby supply current to theenergy storage mechanism 12. Furthermore, there is also the possibilityof supplying electric power to the electric machine 10, as an electricvehicle brake.

A fuel cell system 14 is connected or connectable to the electric energystorage mechanism 12 either directly or preferably via the electriccontrol unit 30. For starting the fuel cell system 14, it obtainselectric current from the energy storage mechanism 12. After the fuelcell system 14 has reached operating status, e.g., it has reached theoperating temperature required for internal reactions, it is itselfcapable of generating power, which can then be supplied to the energystorage mechanism 12. Furthermore, an electric connection of the fuelcell system to the electric side of the electric machine 10 and/or tothe electric side of the generator 40 may also be provided, preferablyvia the control unit 30, to supply the fuel cell system 14 with electricpower to start it or to supply the electric machine 10 with electricpower from the fuel cell system 14.

As in FIG. 1, the internal combustion engine 6 in FIG. 2 is again themain power generator for the drive of the vehicle. The fuel cell system14 is designed as an auxiliary power source for delivering a lower powerthan the internal combustion engine 6. Through the control unit 30, thefuel cell system 14 is operated continuously in a predeterminedoperating range or at a predetermined operating point of high efficiencywhenever the fuel cell system is turned on; the power deliverable by thefuel cell system can be supplied to one or more predetermined devices ofthe power consuming devices, any excess power generated by the fuel cellsystem 14 being supplied to at least one other unit of these powerconsuming devices, depending on the power demand of the device, in orderto maintain the high power delivery by the fuel cell system 14 requiredfor good efficiency.

The excess energy generated by the fuel cell system 14 is preferablyused to drive the vehicle or is stored in the energy storage mechanism12. The maximum efficiency of the fuel cell system 14 is preferably inthe predetermined operating range or at the predetermined operatingpoint. Secondary units 22 and/or 24 may also be provided in FIG. 2, asin FIG. 1.

The excess power of the fuel cell system 14 in FIG. 2, like that in FIG.1, may be supplied either completely or partially to the energy storagemechanism 12 or to the electric machine 10 when the latter is operatedas an electric driving motor, depending on the operating criteria. Suchoperating criteria include, for example, the charge capacity of theenergy storage mechanism 12 and its instantaneous charge status and theinstantaneous power demand of the electric machine 10. It can be seenfrom this that the electric power of the fuel cell system 14 can besupplied only to the energy storage mechanism 12 or, according toanother embodiment, it may also be supplied simultaneously oralternatively to the electric machine 10.

According to a preferred embodiment, the fuel cell system 14 is designed(with respect to its maximum deliverable power) only for the maximumpower demand of the vehicle electric system and/or at least one of thesecondary units or all the secondary units 22, 24 which are not providedfor delivering driving power.

The fuel cell system 14 thus functions only as an auxiliary power unitwhile the internal combustion engine 6 is the main source of drivingenergy. The fuel cell system 14 is at peak efficiency when a consumerthat withdraws from the fuel cell system its maximum generable power isconnected to the fuel cell system.

In FIG. 1 and FIG. 2, the fuel cell system 14 is designed to permit astanding supply (shutdown of the vehicle and/or shutdown of the internalcombustion engine 6). The fuel cell system 14 generates enough currentwhen the vehicle is shut down, in particular when the internalcombustion engine is shut down, in operation of the most importantsecondary units 22 and/or 24 to maintain at least the minimum chargestatus of the energy storage mechanism 12 and/or for a renewed startingof the fuel cell system 14 and to start the internal combustion engine6.

This invention is explained in greater detail below with reference toFIG. 3. It shows the efficiency η of the fuel cell system 14 as afunction of the power “P” generated by it for all the embodiments ofthis invention.

The fuel cell system 14 has its best, i.e., maximum, efficiency η_(max)at a system-determined optimum energy delivery level. This requires anoptimum power demand P₀ of the at least one power consuming deviceconnected to the fuel cell system 14. This yields an optimum operatingpoint “B.” The fuel cell system 14 is designed for the maximum powerdemand P_(max) of the vehicle electric system and the secondary units22, 24. According to this invention, at both optimum power demand P₀ andat a reduced power demand P₁, the fuel cell system 14 is operating atthe optimum operating point “B” at which the maximum efficiency η_(max)prevails or it is operating in an operating range that is close to theoptimum operating point “B” or is close to or includes that point. Thisis achieved by the fact that at a reduced power demand P₁, the excesspower ΔP generated (difference between the reduced power demand P₁ andthe optimum power demand P₀ at the maximum efficiency ηmax) is deliveredto the at least one electric machine 8 and 10 for driving operation orto the energy storage mechanism 12. The optimum energy, i.e., power P₀at which the maximum efficiency η_(max) prevails based on the systemamounts to 2.5 kW, for example, for a passenger vehicle. Depending onthe type of vehicle, the value may be between 1.5 kW and 5.0 kW, forexample. At an optimum power (optimum power demand) P₀ of 2.5 kW and areduced power demand P₁ of 0.6 kW, this yields an excess power of 1.9kW, which can be used directly for driving operation or can be storedtemporarily in the energy storage mechanism 12.

This prevents the fuel cell system 14 from being operated in anoperating range of low efficiency. If the optimum operating point “B”cannot be situated in the range of the maximum efficiency η_(max), it ispreferably shifted in the direction of the maximum power demand P_(max)rather than in the direction of the reduced power demand P₁ because theefficiency curve, starting from the maximum efficiency η_(max), dropsmuch more steeply toward the bottom than toward the top.

The fuel cell system 14 is designed only for a power great enough toensure a basic supply for minimum operation of the motor vehicle, e.g.,for starting the internal combustion engine and for starting the fuelcell system and the lighting system needed for operation of the vehicle.Preferably, however, the basic power supply of the fuel cell system 14is also used to supply power for vehicle devices such as the airconditioning system and/or secondary units as mentioned above.

This invention yields the following advantages, for example, high energysavings, high total efficiency of the motor vehicle due to fuel cellpower supply and recuperation of electric power by operation of one ormore electric machines as a generator which can be driven by the vehiclewhen coasting and/or by the internal combustion engine; power supplywhen the vehicle is standing still, in particular when the internalcombustion engine is turned off, which is particularly low noise,effective and environmentally friendly; relieving the burden on theenergy storage mechanism 12 so that the latter has a greater lifetime;purely electric drive of the vehicle on a permanent basis is alsopossible as long as only low power levels are required; all the knownadvantages of a hybrid drive are preserved.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1. Motor vehicle, with a hybrid drive device having an internalcombustion engine, at least one electric machine at least one electricenergy storage mechanism; a fuel cell system for generating electricpower, wherein the fuel cell system is an auxiliary power source fordelivering a lower power than the internal combustion engine; a controlunit controls the operation of the fuel cell system to operatecontinuously in a predetermined operating range or at a predeterminedoperating point of a high efficiency, with the power the fuel cellsystem delivers being supplied at least to one power consuming deviceand any excess power of the fuel cell system being supplied to at leastone additional power consuming device as required to maintain high fuelcell system efficiency.
 2. Motor vehicle as claimed in claim 1, whereinthe excess power of the fuel cell system is supplied at least partiallyinto the at least one energy storage mechanism so that the latterfunctions as the additional power consuming device.
 3. Motor vehicle asclaimed in claim 1, wherein the excess power can be at least partiallysupplied to the at least one electric machine as driving power, so thatthe electric machine serves as the additional power consuming device. 4.Motor vehicle as claimed in claim 1, wherein at least some of the excesspower of the fuel cell system can be supplied at least partially to theat least one electric machine and the at least one energy storagemechanism as a function of at least one operating criterion so that atleast one of these devices serve as the additional power consumingdevices.
 5. Motor vehicle as claimed in claim 4, wherein the at leastone operating criteria include a drive power demand of the motorvehicle, charge status and maximum charge capacity of the at least oneelectric energy storage mechanism.
 6. Motor vehicle according to claim 1wherein the fuel cell system maximum deliverable power is approximatelyequal to the maximum power demand of the vehicle electric system and ofat least one secondary unit which does not deliver any driving power. 7.Motor vehicle as claimed in claim 6, wherein the at least one secondaryunit an air conditioning system, interior heating, seat heating,cigarette lighter, radio, television, navigation system, data processingsystem, ice chest, refrigerator, window opener, door opener, sunroofopener, convertible top opener, trunk opener, vehicle steering, vehiclebrake system, vehicle interior lighting, vehicle exterior lighting,telecommunications system, compressor, oil pump, water pump, gasolinepump, a tool unit, a cable winch vehicle lift or street sweeper brush.8. Motor vehicle as claimed in claim 1, wherein the predeterminedoperating range or operating point is at or near the maximum efficiencyof the fuel cell system.
 9. Method for operating a motor vehicle with ahybrid drive device having an internal combustion engine, at least oneelectric machine, a fuel cell system for generating electric power whichdelivers a lower power than the internal combustion engine, and at leastone electric power storage mechanism, comprising the steps of activatingthe fuel cell system; operating the fuel cell system continuously in anoperating range or at an operating point of high efficiency; supplyingat least a portion of the power generated by the fuel cell system to atleast one power consuming device; supplying any excess power generatedby the fuel cell system to at least one other power consuming device inorder to maintain a power demand on the fuel cell system correspondingto high efficiency operating range or operating point.
 10. Method asclaimed in claim 9, wherein the excess power of the fuel cell system isstored at least partially in one of the at least one energy storagemechanisms.
 11. Method as claimed in claim 9, wherein the predeterminedoperating range or operating point is at or near the maximum efficiencyof the fuel cell system.